The Migration Of Aging Plastics In Aquatic Environment And Their Environment Behavior With The Typical Antibiotics

Plastics are widely used in varied fields such as aerospace,industry,agriculture,daily life and other fields due to the great convenience such as the light weight,high plasticity,low cost and high durability.According to recent estimates,more than 240 million tons(Mt)of plastic products are consumed.However,only a small part(<26%)is recycled,and a significant proportion is released directly into the aquatic environment.After entering the environment,plastics inevitably undergo physical and chemical interactions to be broken into microplastics or even nanoplasstics.Besides,the personal cleaning products are also an important source of micro/nano plastics.Currently,there is no effective technologies to remove them,thus resulting in a constant increase of micro/nano plastics amount,which have been widely detected from various aquatic system.As an emergent contaminant,micro/nano plastics have the characteristics of small size and large specific surface area,and the pollution they caused had attracted more and more attention.After entering the environment,micro/nano plastics will inevitably undergo ultraviolet radiation,pthotothermal hydrolysis and biodegradation,which will change their chemical composition and structure,such as discoloration,brittle,worsen strength,surface roughness,which is called micro/nano plastics aging.Compared with the pristine micro/nano plastics,the physicochemical properties of aging micro/nano plastic may change,which may affect their migration,adsorption,photolysis and biotoxicity behaviors et al in the environment.Aging is considered as one of the major environmental fate of micro/nano plastics in nature.Strictly,aged micro/nano plastics are more in tune with their actual form in natural environment.Therefore,it is of ecological and practical significance to study the environmental behavior of aging micro/nano plastics.Considering aging is a relatively slow process,fenton,persulfate and non-thermal plasma were selected to simulate and accelerate the aging process of plastic particles,which were represented by F-PS,N-PS and aMPs,respectively,the pristine nanoplastics and microplastic were represented by P-PS and MPs.Spherical polystyrene particles(PS)were selected as the model plastics for their frequent detection in aquatic environment.The second-generation quinolone antibiotic ciprofloxacin(CIP)was selected as a typical contaminant.Environmental behaviors such as migration,adsorption,photolysis and biological toxicity of plastics before and after aging were explored.The main conclusions are as follows:(1)After aging,the surface of nanoplastics(NPs)were rougher;and the surface chemical compositions were changed,a large number of oxygen-containing functional groups such as C-O,C=O and O-C=O were introduced.After fenton and persulfate treatment,the C/O ratio of NPs decreased from 10.98 to 7.25 and 8.58,and CI values increased from 0.085 to 0.38 and 0.45.Hydrophilicity,electronegativity and hydrodynamic diameter increased.These changes in physicochemical properties affected the mobility of NPs.The aging NPs exhibited a higher mobility in saturated quartz sand column,especially in 10 mM NaCl solution,the mobility of F-PS and NPS increased from 79.73%to 90.97%and 95.67%.We used DLVO and XDLVO theory to further explain the interaction force between NPs and NPs and between NPs and quartz sand,respectively.It is found that the maximum total interaction energy(ΦTOT)between P-PS,F-PS,N-PS increases successively,and the main interaction force between P-PS and quartz sand is double electric layer electrostatic repulsion(ΦEDL).The main force between F-PS,N-PS and quartz sand is ΦEDL and Lewis acid-base force(ΦAB).In F-PS and N-PS,ΦAB changes from repulsive force to attraction force,for the weak hydrophobic effect of F-PS and N-Ps,which is more favorable for them to adhere to quartz sand.(2)Non-thermal plasma(NTP)was used to accelerate the aging process of microplastics(MPs),the environmental behaviors of MPs and aMPs with CIP were investigated,including adsorption,photolysis and biotoxicity.The results showed that after NTP treatment,the surface of aMPs become rougher;the benzene ring structure broke,a large number of oxygen-containing functional groups were introduced,and the C/O ratio decreased from 39.32 to 12.59;hydrophilicity and electregativity significantly enhanced,particle size and crystallinity decreased.The adsorption experiment showed that the adsorption equilibrium capacity significantly improved from 0.3725 to 0.5587 mg/g at 5 mg/L,increasing about 49.99%.Moreover,the different environmental factors such as pH,salinity,organic matter have a greater impact on adsorption performance of aMPs than pristine MPs.Photolysis experiments show that aMPs have a weak promoting effect on CIP photolysis,while the pristine MPs may have a certain inhibitory effect due to the weak light-blocking effect.The single toxicity test of MPs,aMPs and CIP on Escherichia coli(E.coli)growth showed different effects.The pristine MPs had no effect on E.coli growth due to their chemical inertia,while the 40 mg/L aMPs and 2 μg/L CIP showed significant inhibitory were 20.37%and 42.36%,respectively.The joint toxicity showed slight ’2<1+1’ effects(～3.5%)may ascribe to the adsorption effect.Transcriptome data showed that the number of differential genes(DEGs)was positively correlated with biotoxity,and the DEGs were mainly enriched in the processes of oxidative stress and membrane permeability.The increase of reactive oxygen species(ROS)and membrane permeability,the qPCR results verified the reliability of transcriptome.